Identifying regions of strong scattering at the core–mantle boundary from analysis of PKKP precursor energy

Abstract

We detect seismic scattering from the core–mantle boundary related to the phase PKKP (PK• KP) in data from small aperture seismic arrays in India and Canada. The detection of these scattered waves in data from small aperture arrays is new and allows a better characterization of the fine-scale structure of the deep Earth especially in the southern hemisphere. Their slowness vector is determined from array processing allowing location of the heterogeneities at the core–mantle boundary using back-projection techniques through 1D Earth models. We identify strong scattering at the core–mantle boundary (CMB) beneath the Caribbean, Patagonia and the Antarctic Peninsula as well as beneath southern Africa. An analysis of the scattering regions relative to sources and receivers indicates that these regions represent areas of increased scattering likely due to increased heterogeneities close to the CMB. The 1 Hz array data used in this study is most sensitive to heterogeneity with scale lengths of about 10 km. Given the small size of the scatterers, a chemical origin of the heterogeneities is likely. By comparing the location of the fine-scale heterogeneity to geodynamical models and tomographic images, we identify different scattering mechanisms in regions related to subduction (Caribbean and Patagonia) and dense thermo chemical piles (Southern Africa).